ZisaLog: Beginner’s Guide to Building a Custom PC 
When studying about PC parts to build a custom PC, many people wonder, “Memory and storage both save data, so what is the difference? Why are they separated?”
This article explains the differences between memory and storage, and the reasons why they are separated.
- Memory is responsible for temporary data storage, while storage is for long-term data storage.
- Memory is volatile and loses data when the power is off, but storage is non-volatile and keeps data.
- Memory allows very fast data access, while storage is slower than memory.
- Memory is high-cost and has less capacity, but storage is low-cost and can have large capacity.
- Memory is optimized for parallel processing and low latency, while storage is optimized for large capacity storage.
- Memory has high write endurance, but storage (especially SSDs) has a limit on the number of writes.
- Memory fills the speed gap between the CPU and storage to support fast CPU processing.
- Frequently used data is saved in memory, allowing quick re-access.
- Memory and storage utilize each other’s strengths to optimize overall PC performance.
This explanation assumes basic knowledge about memory and storage, so reading the following articles before this one will help deepen understanding.
≫ Related Article: How to Choose Memory for a Custom PC [Performance / Features / Compatibility]
≫ Related Article: How to Choose Storage (SSD/HDD) for a Custom PC [Performance / Features / Compatibility]
Select PC parts and online stores to instantly generate an estimate, check compatibility, and calculate power requirements. You can save up to five different builds, making it easy to try out multiple configurations.
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Table of Contents
Differences Between Memory and Storage
Memory and storage are both parts that record data, but their roles and the period they can store data are different.
List of Differences Between Memory and Storage
Here is a summary of the differences between memory and storage by category.
| Item | Memory (RAM) | Storage (SSD/HDD) |
|---|---|---|
| Role | Temporary data storage | Long-term data storage |
| Volatility | Volatile Data is lost when power is off | Non-volatile Data is kept even when power is off |
| Speed | Very fast | Slower than memory |
| Capacity (per price) | Small | Large |
| Cost (per capacity) | High cost (expensive) | Low cost (cheap) |
| Design | Optimized for parallel processing and low latency | Optimized for large data storage |
| Endurance | High write endurance | Write cycle limit |
| Power Consumption | Low power consumption | High power consumption (especially fast SSDs) |
| Usage Example | Temporary storage of data and programs needed when running applications | Storage of OS, applications, and personal data |
| Types | DRAM (regular memory) SRAM (cache memory) | HDD, SSD |
Now, let’s look at each point simply.
Difference in Roles
Memory temporarily stores and accesses data.
It temporarily saves data needed by currently running applications and processes, allowing the CPU to access it quickly.
Mainly, it supports holding active work data and fast data access.
On the other hand, storage saves data for the long term.
It stores system data like the OS, applications, user data such as photos and videos, and files created with office software.
Difference in Volatility
Memory is volatile, so data stored in it is lost when the power is off.
Memory is optimized for short-term data storage, and when restarting a PC, data needs to be reset to maintain data integrity.
Storage is non-volatile, so data is kept even when the power is off.
It is designed for long-term data storage, so data can be read and referenced even after restarting the PC.
Difference in Speed
Memory can read and write data very fast, about 20–60GB/s.
This speed is essential for the CPU to quickly get and process data.
Memory can access data instantly with low latency, which improves overall system performance.
Also, memory has high parallel processing ability, so it can keep performance even if many processes or threads access it at the same time.
In contrast, storage is slower than memory, and even the fastest NVMe SSD is about 3–10GB/s.
For reference, SATA SSDs are about 500MB/s, and HDDs are about 150MB/s, which are different units.
Recently, NVMe SSDs have become much faster, but even then, the fastest SSD (about 10GB/s) is still half as fast as the slowest memory (about 20GB/s).
For reference, SATA SSDs are about 500MB/s, and HDDs are about 150MB/s, which are different units.
Among storage devices, NVMe SSDs are very fast, but still not as fast as memory.
Difference in Capacity and Cost
Memory has a high manufacturing cost to provide fast data access, so the price per capacity is high.
The design is complex to achieve high speed and low latency, which increases manufacturing cost.
On the other hand, storage is relatively low-cost and can have large capacity.
Especially HDDs are very cheap and can store a lot of data, but recently SSD prices are going down, making a good balance between performance and capacity.
Difference in Design
Memory is designed for high parallel processing ability and low latency.
This allows the system to keep performance even when many applications or processes run at the same time.
Storage is optimized for data reliability and persistence, so it can store large amounts of data for a long time.
HDDs are good for large data storage, and SSDs combine fast access and durability.
However, storage does not have high parallel processing ability, so if many processes access it at the same time, conflicts can happen and latency increases.
Difference in Endurance
Memory can withstand frequent writing, and is made for use in applications or processes that read and write data often.
On the other hand, storage, especially SSDs that use flash memory, has a limit on the number of writes.
If the number of writes increases, the flash cells wear out, and eventually the SSD’s lifespan becomes shorter.
Reasons for Separating Memory and Storage
The reasons for separating memory and storage are the speed difference, cost, and efficient data transfer between the CPU and storage.
The CPU Needs Fast and Quick Data Exchange
The CPU, memory, and storage (SSD/HDD) are all PC parts with different roles.
The CPU processes and calculates data very fast, but to use its full performance, fast and quick access to data is essential.
Memory is designed to meet this need, temporarily saving data and programs the CPU needs so it can access them quickly.
It can read and write data very fast, about 20–60GB/s, making it the only storage device that can keep up with the CPU’s speed.
On the other hand, storage is used to save data for a long time, but its access speed is not as fast as memory.
So, if the CPU reads and writes data directly from storage, the CPU has to wait, and the whole PC’s performance drops.
Fast Memory Acts as a Cushion Between CPU and Storage
To prevent the fast CPU from having to wait, memory helps with data exchange between the CPU and storage.
Memory acts as a cushion to prevent performance drops caused by the speed difference between the fast CPU and (from the CPU’s view) slow storage.
Specifically, when loading data from storage, it is first loaded into memory.
This allows the CPU to quickly get the needed data from memory and continue processing.
Also, data and programs that the CPU accesses often are temporarily saved in memory, so the access time to these data is greatly reduced.
Because frequently used data is saved in memory, from the second time on, the needed data can be read from memory for even faster access.
So, the CPU can keep fast processing without being affected by storage delays.
Also, after the CPU processes data, the result is temporarily saved in memory.
Then, at the right time, data is written from memory to storage, so the CPU’s processing is not interrupted and goes smoothly.
This process makes data transfer between the CPU and storage efficient, optimizing the whole PC’s performance.
Memory supports fast CPU processing with high data transfer speed and low latency.
At the same time, storage supports large data storage and persistence with non-volatility.
By using their strengths together, memory and storage allow the PC to work fast and efficiently overall.
Summary: Memory and Storage in the Right Place
Memory and storage are both parts for saving data, but looking at their differences shows they have very different features.
Here are the key points again.
- Memory is responsible for temporary data storage, while storage is for long-term data storage.
- Memory is volatile and loses data when the power is off, but storage is non-volatile and keeps data.
- Memory allows very fast data access, while storage is slower than memory.
- Memory is high-cost and has less capacity, but storage is low-cost and can have large capacity.
- Memory is optimized for parallel processing and low latency, while storage is optimized for large capacity storage.
- Memory has high write endurance, but storage (especially SSDs) has a limit on the number of writes.
- Memory fills the speed gap between the CPU and storage to support fast CPU processing.
- Frequently used data is saved in memory, allowing quick re-access.
- Memory and storage utilize each other’s strengths to optimize overall PC performance.
The CPU needs fast and quick data exchange, so memory sits between the fast CPU and (from the CPU’s view) slow storage to fill the speed gap.
By using their features together, memory and storage support CPU processing, resulting in high performance for the whole PC.
≫ Related Article: How to Choose Memory for a Custom PC [Performance / Features / Compatibility]
≫ Related Article: How to Choose Storage (SSD/HDD) for a Custom PC [Performance / Features / Compatibility]
Select PC parts and online stores to instantly generate an estimate, check compatibility, and calculate power requirements. You can save up to five different builds, making it easy to try out multiple configurations.
≫ Tool：PC Parts Estimation & Compatibility Check Tool
